<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
    <title>测试页面</title>
    <link href="https://fonts.font.im/css?family=Open+Sans" rel="stylesheet" type="text/css"> 
</head>
<body>
    <h1>Hello world!</h1>
    <button id="bt_1">变为红色</button>
    <button id="bt_2">复原</button>
    <script src="scripts/main.js" defer></script>
</body>
</html>